This invention relates in general to monitoring systems and, more particularly, to a method and apparatus for mapping the physical position of an object from a video image to a map of a monitored area.
A surveillance or monitoring system may include a video camera which generates images of a monitored area or region, and a computer which receives and processes the images from the video camera. The computer includes a digitized map, and monitors the detected video images in order to determine the presence in the monitored area of an object of interest, such as a human. When an object of interest is identified through analysis of the detected images, the location of the object is mapped from the image to the map.
This known system includes a computer-aided drafting (CAD) model of the environment or monitored area, which serves as the basis for the map. Further, in order to accurately determine the location on the map of an object identified in the detected images, parameters of the camera must be determined, and must be introduced into the computer. The camera parameters include not only internal parameters such as focal length and the number of millimeters per pixel, but also external parameters such as the location and the orientation of the camera.
When this known system is in operation, the location on the map of an object in a video image is determined using a formula derived by inverting equations that describe image formation geometry. The necessary set up and initialization for this system is complex and time consuming. Determining all of the pertinent internal and external parameters of the camera, and entering them into the computer system, is a complex and time-consuming task. Also, preparing the CAD model of the monitored area can be a slow and time-consuming task.
In addition, even if care is exercised in the determination of the camera parameters and the preparation of the CAD model, errors can still occur. For example, an object which is visible to the camera, because it is on a side of a wall nearest the camera, may be incorrectly positioned on the map on the opposite side of that wall, where it would not actually be visible to the camera. Errors of this type become even more problematic if the camera parameters and CAD model are not carefully established.
From the foregoing, it may be appreciated that a need has arisen for a method and apparatus for mapping an object in a detected image to a map of the monitored area, which permit the mapping function to be easily and rapidly defined with minimal possibility for error, while avoiding the need to obtain and input both internal and external camera parameters.
According to the present invention, a method and apparatus are provided to address this need, and involve: providing a map of a monitored area; detecting a reference image of the area; identifying a first region which corresponds to a selected portion of the area as viewed in the reference image; identifying a second region which corresponds to the selected portion as viewed on the map; detecting a further image of the area; identifying a portion of the further image corresponding to an object of interest; selecting in the region of the lower end of the portion of the further image a first point which is within the first region; and carrying out a warp transformation of the first point from the first region to the second region, in order to identify within the second region a second point which corresponds to the first point and which identifies a position on the map of the object of interest.